Process of recovering metals from silicates



FRANCIS M. MGCNAHAN, 01E 5* n w, rnn'nsrnvan'ra.

PROCESS 0E REGOVEEING MET FROM SILICA'EES.

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T 0 all whom it may concern Be it known that T, FRANCIS M. MCCLEN- AHAN, a citizen of the United States, and a resident of Oakmont, in the county of Allegheny and State of Pennsylvania, have invented a new and useful Improvement in Processes of Recovering Metals from Silicates, of which the following is a specification. i

The invention relates to the recovery of metals, particularly aluminum and potassium,,f1-om silicates containing them, and has particularly to do with the breaking up of double ammonium-aluminum fluorides formed in the process of recovering from aluminous silicates such as kaolin, feldspar, leucite, glauconite, etc., metals whose silicofluoride or whose hydroxides are practically insoluble in an aqueous solution of ammonium fluorides and ammonium hydroxide, which process is disclosed in my pending application Serial No. 432,518, filed December 22, 1920.

According to the process disclosed in said application and contemplated herein. ground or otherwise pulverized silicates of aluminum to which water is preferably added to form a pasty or semi-fluid mixture, is decomposed by the addition of a fluoride of ammonium in excess of that theoretically required to reduce the constituent elements to an aqueous solution of fluo-silicates contain ing hydrated oxide of aluminum as a precipitate. This decomposition is eflected preferably at about the boiling temperature of the mixture. While the fluoride of ammonium may be neutral, basic or acid, it is preferred to use acid ammonium fluoride, commercially known as ammonium bi-fluoride. The silicates require no treatment previous to their being mixed with the fluoride of ammonium, it being only necessary from a practical standpoint that they be sufliciently pulverized to permit them to be freely and rapidly decomposed.

When feldspar is so decomposed the re action may in part be expressed by the following equation 16NH F+10H O In addition to this reaction it has been found that a series of chemical reactions take place giving rise to the presence of double ammonium-aluminum fluorides such as Specification of Letters Patent. m nm A 22, 11 2 Application filed December 7; 1921; Serialffl'o. 520,601.

AIF BNILF, the tenacity of the union of which is very pronounced. The following equation expresses the chemical reaction which may take place incident to the formation of such double ammonium-aluminum fluorides.

The double ammonium-aluminum fluoride is formed by a portion of the ammonium fluoride (NH F) of the right hand portion of the equation uniting with the aluminum fluoride (AlF The object of the present invention is to improve the process thus explained to the end that the tenacious double ammonium-aluminum fluorides may be broken up readily and aluminum recovered as a hydrated oxideand potassium as a silico-fluoride. A further object is to provide an improved process of hydrolyzing double ammonium-aluminum fluorides regardless of how they may be formed.

In the practice of this invention the precipitate of equations 1 and 2 is heated in the presence of water to a temperature sufficiently high to cause the aluminum fluoride of the double ammonium-aluminumfluorides to decompose. This decomposition is attended by the formation of hydrated aluminum oxide and hydrofluoric acid, the latter of which unites with the ammonium fluoride of the original double ammonium-aluminum fluorides to form ammonium bi-fluoride, which, at the temperature of the reaction is vapor. To prevent the ammonium bi-fluoride vapor from reacting with the hydrated aluminum oxide it is continuously removed from the receptacle in which the double ammoniumaluminum fluorides are treated, The reaction which takes place in this treatment may be expressed by the following equation:

Before the precipitate resulting from the reactions of equations 1 and 2 is treated in the manner described, it may, if desired be washed in hot water to remove the ammonium silico-fluoride which ordinarily adheres quite closely to the sludge, and the resulting sludge and liquor may be separated in a settling tank. While the moist sludge may then be placed in a retort and heated either indirectly by external heat or directly by passing hot air or steam through it to hydrolyze the double ammonium-aluminum fluorides, the

sludge is preferably first dried and then heated in a.suitab.le retort by passin super the liberated vapors from the mass and the retort. By agitating the mass and removing the liberated hydrofluoric acid and ammonium fluoride vapors, the steam prevents subsequent reaction of these vapors upon the hydrated aluminum oxide.

The liberated and removed vapors may be subsequently condensed, preferably by passing them into water. The hydrofluoric acid and ammonium fluoride combine to form Water soluble ammonium bi-fluoride, while the wai er insoluble potassium silico-fluoride forms a sludge which may easily be separated from the aqueous condensate. In case the ammonium silicofluoride is not Washed or otherwise removed from the preciipitate of equations 1 and 2, it too will pass 0 as a vapor from the mass when heated in the manner described, and subsequently may be condensed and separated from the condensed ammonium bi-fluoride.

' At the completion of the heating operationthe treated mass is hydrated aluminum oxide, with which there may be mixed small quantities of impurities such as mica, free silica, iron oxide, etc., which may be present in the silicates originally digested. The filtrate of equations 1 and 2 may be treated in the manner disclosed in my above identified "application.

-While the invention'has been explained chiefly with reference to its applicability to the recovery of alumina from silicates containing them, it'is also applicable to the recovery of hydrated oxide of aluminum from double ammonium-aluminum fluorides regardless of Whether they are formed in the digesting of silicates by a fluoride of ammonium.

I claim as my invention: 1. The process of recovering metals from silicates containing them, which comprises decomposing the silicates by a fluoride of ammonium, separating the resulting precipitate from the liquor, and simultaneously heating the precipitate in the presence of water and removing and condensing the, resultin vapors.

2. e process of recovering alumina from silicates containing them, which comprises decomposingthesilicates by a fluoride of ammonium, separating the resulting precipitate from the liquor, and simultaneously' agitating the precipitate, heating it to temperature of not less than about 300 C, and removing the resulting vapors,.. whereby hydrated oxide of aluminum is formed.

3. The process of recovering alumina from silicates cgntaining them, which comprises decomposing the silicates by a fluoride of am monium, separating the resulting precipimm from the liquor, and simultaneously injecting into the precipitate steam heated to a temperature of not less than about 300 C. and removing the resulting vapors, whereby hydrated oxide of aluminum is formed.

4. The process of recovering metals from silicates containing them, which comprises decomposing the silicates by an excess of ammonium bi-fluoridev in the presence of Water, separating the resulting precipitate from the liquor, drying the precipitate, and simultaneously passin 90 through the dried precipitate steam heated to a temperature of not less than about 300 C, and removing the resulting vapors.

5.-The process of recovering hydrated oxide of aluminum from an intimate mixture of aluminum and ammonium fluorides, which comprises heating said mixture in the presence of Water and simultaneously removing the resulting vapors.

6. The process of recovering hydrated oxide of aluminum from an intimate mixture of aluminum and ammonium fluorides, which comprises simultaneously agitating and heating the mixture and removing the resulting vapors.

7. The process of recovering hydrated oxide ofaluminum from an intimate mixture of aluminum and ammonium fluorides, which comprises simultaneously heating the mixture to a temperature of not less than 110 about 300 'C., agitating it and removing the resulting vapors.

8. The process of recovering hydrated oxide ofaluminum from an intimate mixture of aluminum and ammonium fluorides, 115 which comprises passing through said mix.- ture steam heated to a temperature of not less than about 300 (3., and simultaneously removing the resulting vapors.

9. The process of hydrolyzing double am- 

